1. Field of the Invention
The invention relates to V-grooved pulleys for use with the endless drive belt of a vehicle accessories drive system. More particularly, the invention relates to a composite pulley in which the body of the pulley is formed of sheet metal and a unique multi-V-groove belt-receiving formation is molded of plastic on an outer cylindrical wall portion of the metal body.
2. Description of the Prior Art
There is a trend today in the automobile industry to operate the various vehicle accessories such as the power steering pump, air pumps, air conditioning and alternator by a single endless drive belt driven by a pulley connected to the engine crankshaft. This system is referred to as a "serpentine" drive belt system. This has resulted in the need for strong, efficient and reliable operating pulleys for driving the various vehicle accessories by their connection to the serpentine drive belt. These pulleys must have accurately formed V-grooves, dynamic pulley balance, and thick, rigid and strong areas in which the pulley grooves are formed.
Heretofore, such multi-V-grooved pulleys were formed completely of metal. A cup-shaped blank was either die stamped or roller spun from metal sheets with the V-grooves being subsequently stamped, slit or roller spun in an outer wall portion thereof. Examples of such all-metal pulleys are shown in U.S. Pat. Nos. 2,869,223, 3,908,421, 3,995,474 and 3,991,598.
These spun metal pulleys are formed with the usual single, double or triple V-shaped belt-receiving grooves in which the V-groove-forming walls are either equal in thickness or thinner than the thickness of the parent metal of the pulley wall in which the grooves are formed. Also, these prior art grooves have generally rounded crests and valleys between adjacent grooves and are adapted to receive a plurality of individual drive belts having the usual inverted trapezoidal cross-sectional configurations and not the particular cross-sectional configurations of the serpentine drive belts.
One known pulley which has been produced for use with these serpentine drive belts known in the art as a poly-V-pulley or poly-V-grooved pulley and which eliminates many of the problems and difficulties encountered with prior pulleys is shown in U.S. Pat. No. 3,977,264 entitled Method of Making Poly-V-pulleys and Product. This patent discusses the problems and difficulties that are involved in forming a satisfactory pulley construction having the required multi-V-groove belt-receiving formation in an outer portion thereof for the serpentine drive belts. Although pulleys formed by the metal-working procedure of U.S. Pat. No. 3,772,928 provide a satisfactory and efficient pulley, it is believed that a composite pulley formed of plastic and metal provides a construction which is less expensive, lighter in weight, and has strength comparable with the all-metal pulleys heretofore used.
Composite pulleys formed of plastic and metal are not new, per se. U.S. Pat. Nos. 3,557,424, 3,651,705 and 3,696,685 illustrate examples of composite plastic and metal pulleys of the type in which the outer pulley surface is formed with a series of teeth for use with a toothed belt drive. U.S. Pat. Nos. 3,772,928 and 3,788,155 are examples of two known composite plastic metal pulleys in which the pulley is formed with a V-groove in an outer portion thereof. The plastic formation in which the V-grooves of these two known pulleys are formed use internal and external metal reinforcement to strengthen the grooves and use a considerable amount of plastic material. Unbalanced pulleys could result with such prior composite constructions if the plastic reinforcing metal tabs or members are not completely uniform and symmetrical throughout the metal body. Also, formation of these tabs requires another manufacturing operation and additional equipment, thereby increasing the cost of the final pulley product. Furthermore, the V-grooves of these two pulleys are of the type having a cross-sectional configuration adapted for receiving individual drive belts having a usual inverted trapezoidal cross-sectional configuration as the heretofore all-metal belt-receiving pulleys.
Accordingly, the need has existed for a new multi-V-groove pulley having a metal, generally cup-shaped body with a unique multi-V-groove belt-receiving formation molded of plastic on an outer wall portion of the metal body which is free of plastic-reinforcing metal tabs, thereby avoiding the difficulties and undesirable characteristics present in prior all-metal multi-V-grooved pulleys and achieving results not obtainable with existing composite plastic metal pulleys.